Crude oil distillation is used to separate petroleum crude into several products, including naphtha, kerosene, diesel and gas oil, for example. Such products of crude oil distillates may either be sent out as final products or may be further processed. Crude oil distillation is not only an indispensable unit in a refinery but is also the largest unit among all petroleum or chemical processing units. One of the major objectives of crude oil distillation design and operation is to increase the amount of distillate products, because the distillate products are much more valuable than the residue. However, the yield of distillates is limited by the allowable maximum temperature, above which substantial thermal cracking takes place, thereby resulting in loss of product and fouling of equipment.
In an atmospheric-vacuum distillation system with both atmospheric tower and vacuum tower, it is economically desirable to increase the amount of atmospheric distillates and reduce the atmospheric residue, which feeds the vacuum tower. On the basis of one barrel distillate product, vacuum distillation requires extra energy to maintain a vacuum system. Energy is required to remove leaked air, non-condensables in the oil and light olefins formed by thermal cracking. On the basis of the same capacity, a vacuum tower would be much larger in size and therefore more expensive because one pound of vaporized oil at 10 mmHg absolute pressure requires a space about 70 times larger than that required at atmospheric pressure.
Therefore, there exists a need in the art for new and improved methods of crude oil separation that increase the yield of products such as diesel and gas oil and therefore overcome the disadvantages and defects of the prior art.